1. Field of the Invention
The present invention relates to an image forming apparatus that is disposed with a photosensitive body and a processing device and forms an image on a recording medium, and to a process cartridge that is disposed with a photosensitive body and a processing device and is loadable in and unloadable from an image forming apparatus mainframe.
2. Background Art
Conventionally, as a multicolor image forming apparatus that forms a multicolor image of four colors on a recording medium such as recording paper, a so-called tandem-system device is known where photosensitive bodies, exposure means that expose the photosensitive bodies to form electrostatic latent images on the surfaces of the photosensitive bodies and developing means that supply a charged developing agent to the surfaces of the photosensitive bodies on which the electrostatic latent images have been formed are respectively disposed in line in numbers corresponding to the number of colors (e.g., the four colors of magenta, cyan, yellow and black). A 4-cycle-system device is also known where there is one exposure means and one photosensitive body, with developing means being disposed around the periphery of the photosensitive body in a number corresponding to the number of colors.
Here, the latter 4-cycle system is not suited for increases in the speed of image formation because steps such as exposure and development of the photosensitive body are conducted by successively changing the colors. In contrast, with the tandem system, steps such as exposure and development of the photosensitive body can be conducted substantially simultaneously for each color, and a multicolor image can be formed by successively superposing and transferring, to the recording medium, the developing agent adhering to the photosensitive bodies corresponding to the colors. For this reason, a tandem-system multicolor image forming apparatus is suited for increases in speed because the sped of image formation is not much different from that in the case of monochromatic image formation.
In these image forming apparatuses, it is necessary to occasionally replace the photosensitive bodies and developing means. In a tandem-system multicolor image forming apparatus, because the exposure means and photosensitive bodies are respectively disposed in numbers corresponding to the number of colors, a contrivance is necessary so that, at the time of replacing the photosensitive bodies and the developing means (there are cases where these are integrally and replaceably configured as process cartridges), these do not interfere with the exposure means. Thus, evacuating the exposure means to a non-interfering position at the time of replacing the process cartridges has been considered (e.g., see JP-A-2001-166555).
However, when the exposure means are evacuated at the time of replacing the process cartridges, the position of the exposure means of each color subtly relatively moves each time replacement is conducted, so that there is the potential for this to cause color shifting.